The present invention relates to processes and apparatuses for checking carburetors for internal combustion engines, of the type comprising an idling circuit opening into the intake passage of the carburetor through an idling orifice placed downstream of the minimum opening position of an operator operable throttle and through bypass aperture means. The bypass aperture means, in the form of a slit or of holes distributed along the intake duct, ensures correct operation of the engine when the driver opens the throttle, generally formed by a butterfly valve, from its minimum opening position.
The wear of the moving parts of the carburetor, essentially the shaft of (or the support for the shaft of) the butterfly valve, causes clearance and lost motion which shifts the edge of the butterfly valve with respect to the bypass aperture means. Since such shifting causes operating abnormalities, it is desirable to detect it. Thus it may be determined if operating defects of the engine are due to wear and, if so, which repairs or replacements must be carried out.
Unfortunately, it is difficult to assess the extent of wear of the shaft or if its support by visual inspection, even during normal maintenance on the vehicle and attendant removal of the air filter, for the extent of wear which is acceptable is small. It is consequently frequently necessary to remove the carburetor and to measure directly the extent of wear. It is also possible to measure air and/or fuel flow rates through the intake duct of the carburetor on a test bench (French Pat. No. 2,354,552). The results are not satisfactory due to the lack of a direct relation between the measurements and the extent of wear, while removal of the carburetor entails immobilization of the vehicle and the required test bench is expensive.
It is an object of the invention to provide a process and apparatus for assessing the wear of the moving parts of a carburetor while on the engine which it supplies; it is a more general object to provide for assessing the wear simply and economically.
According to an aspect of the invention, there is provided a process for assessing the wear of relatively movable parts of a carburetor in which the associated engine is operated while holding the throttle of the carburetor in a position where it defines a passage of predetermined cross-section for which, when the carburetor is new, the edge of the throttle is astride the bypass aperture means and the degree of vacuum in the idling circuit of the carburetor is compared with a reference value which is that which prevails, under the same operating conditions, in the carburetor when new.
The comparison will generally be carried out by measuring the difference between the pressure in the idling circuit and the pressure in the part which is situated between two calibrated apertures of a passageway which connects an air source at atmospheric pressure to a point in the intake duct downstream of the throttle.
The position of the throttle for the comparison may typically be adjusted while the air flow is determined by measuring the vacuum in the throat of a venturi in the intake duct. That vacuum may be compared with a standard vacuum, taken in the part situated between two calibrated apertures of a passageway connecting the atmosphere to a point downstream of the throttle.
The process is simple because it makes use of the fact new carburetors are factory adjusted, before being mounted on engines so that the vacuum in the idling circuit when the carburetor is new is accurately predetermined and reproducible. This reproducibility removes the need for a flow bench, the engine itself being able to be used as a source of vacuum and circulation pump.
According to another aspect of the invention, an apparatus for implementing the process in a simple way has means for connection with the carburetor associated together in a single hose provided with connectors and possibly with a flowrate measuring venturi which is fixed to the carburetor in place of the air filter.